Since 2013 nearly 50 people, including members of religious minorities, foreigners and liberal activists, have been murdered by Islamist militants, according to Press TV.

More than 11,000 people have been arrested over the past four days in a new crackdown in connection with the attacks.

Islamic State (IS, formerly ISIS/ISIL) and a South Asian branch of Al-Qaeda have claimed responsibility for many of the murders, but the police and government have blamed the Islamist extremist groups Ansarullah Bangla Team (ABT) and Jamayetul Mujahideen Bangladesh (JMB), for most of the killings.

The announcement of the fatwa on Tuesday by Farid Uddin Masuod, head of the Council of Bangladesh Clerics, comes as the country faces increased international pressure to bring the spate of attacks to an end.

Masuod said that more than 100,000 clerics had signed the religious edict which will be made public on June 18.

“The fatwa unequivocally said these killings of non-Muslims, minorities and secular activists are forbidden in Islam,” he stated, as reported by ABNA.

“We’ve said these killings are illegal and are crimes against humanity.”

Masuod believes the fatwa will make a difference as it disparages any Islamic militants that try to defend the killings. “One cannot deny that in Bangladesh, fatwas can have a tremendous impact,” he told the Dhaka Tribune.

The message will be distributed in a pamphlet, through preaching in mosques as well as online and through social media: “We will use Facebook, Twitter, WhatsApp and so on. Because the young generation gets so much misleading information on online platforms, to counter this, online media should be focused on more.”

Confirmation of the fatwa coincided with the fourth day of a nationwide anti-militant drive during which police said they arrested 3,115 people, bringing the total arrested over the short period to more than 11,300.

Some 176 of those arrested are suspected members of Islamist militant groups, according to NDTV. Arms, ammunition, other weapons and more than 2,000 motorbikes were also seized during this week's raids.

Bangladesh police said the arrest on Thursday of a man suspected of attacking a secular publisher, blogger and poet last year is an important breakthrough in the ongoing case.

The latest in this wave of suspected terrorist attacks happened last week when the wife of a top anti-terror police officer was fatally attacked while walking her son to his school bus. The killing is also believed to have sparked a gunbattle between police and alleged militants, resulting in the deaths of five suspected extremists.

Bangladeshi Prime Minister Sheikh Hasina pledged that “each and every killer” would be arrested. However, opposition group, the Bangladesh Nationalist Party (BNP) claims 2,100 of its activists were arrested in the crackdown and accused the government of using the crackdown as an opportunity to suppress political dissent.

The Bangladeshi government have previously separately accused the BNP and the Israeli government of orchestrating the attacks to create political unrest and undermine its authority.